This invention relates generally to a dental prosthesis that is attached to an implant embedded in the bone of a person's jaw, and more particularly to a method, apparatus and device for improving the attachment of the implant to the bone of the jaw and allowing for earlier loading.
Implantation of teeth in the mouth goes back to ancient times, being traced to the Pharaohs in Egypt. Because osseointegration techniques had not yet been discovered, attachments for these implants in the jaw bone were purely mechanical and were not as successful as the present techniques that rely on osseointegration. However, before osseointegration, it was not necessary to wait for prolonged time periods until integration was completed. U.S. Pat. Nos. 2,745,180 and 2,857,670, issued to Kiernan in 1956 and 1958, respectively, provide means for attachment of an implant to the jaw bone structure by means of pins that are forced laterally out from the implant after the implant is inserted in the bone. These pins have pointed ends that, with application of high force, penetrate the bony structure, i.e., the softer spongiosa of the jaw bone, in an effort to make a tooth implant permanent. However, the spongiosa is a relatively soft, living bony material, and subject to changes. Accordingly, reliability and permanence of an implant were not assured.
It is now common when it is desired or necessary to replace a missing tooth, to open the gum and to embed an implant in the bone structure beneath the gum. The implant is held in the bone in a socket hole by friction or the implant may be threaded into the bone. The gum is then closed over the implant and heals. When a proper material is used for the implant, e.g., titanium, the bone grows into the implant by osseointegration so that after several months the implant becomes a part of the bone structure in the mouth.
The procedures, which are followed after osseointegration has advanced, depends upon the dental practitioner's selection of a manufacturer's product. Many devices are available in complete systems of dental implants and prostheses for subsequent attachment to the implants. For example, a system that is widely used by dental practitioners is available from Nobelpharma USA Inc., Westmont, Ill.
In one system, the implant in a typical construction has an axially threaded hole at its top, i.e., the proximal end near the gum. After the bone has joined to the implant, the gum over the implant is reopened to expose the tapped hole. Then, an abutment is threaded into the tapped hole of the implant and extends to a level above the gum. The protruding end of the abutment is constructed with a non-round shape for attachment of a prosthesis. Also, the protruding end includes a central threaded hole extending inward toward the jaw bone.
A false tooth or crown is provided with a hole, known as a chimney, therethrough, and a non-round recess in its base that corresponds in shape to the protruding non-round cross-section of the abutment. Thereby, the crown can be joined to the abutment with a self-aligning connection that prevents relative rotation between them. A screw, passed into the chimney opening, engages the tapped hole in the abutment so as to hold the crown axially to the abutment. Thus, the crown cannot rotate about the abutment because it is fixed into the special contours on the exposed abutment end, and the crown cannot pull away from the abutment when the screw has been tightened in place.
Finally, the chimney above the screw is filled with a composite filler material that hardens and is shaped as part of the crown, to look like a natural tooth.
Such techniques have proven to be highly successful in a rapidly developing art. Implants have lasted ten and more years without replacement and the number of successful implants is in the order of 80%-90% of the implants undertaken. Failures most frequently occur when the implant fails to be properly integrated with the bony tissue of the jaw bone.
A major problem, and a source of patient dissatisfaction, resides in the several months of marked inconvenience for the patient while the process of osseointegration takes place and the implant becomes fixedly attached to the jaw bone. This difficulty, to be overcome, requires an avoidance of eating and chewing foods that will cause undesirable stresses and force transmissions in the tooth region. From present understanding, it appears that osseointegration takes place between the bone and the titanium implant under strict conditions of immobilization and without force or stress applied on the bone/implant interface. An uninterrupted growth of bone on the titanium surface is the time-consuming factor.
However, it is not completely clear at this time whether osseointegration taken place under the condition of extreme immobilization and, if not, how much movement of the implant is tolerable. It is also not clear whether controlled application of force is harmful, or may actually help if applied in a specific manner. From many years of metal implantation in bones, it has been learned that stress sharing constructions made of bone and implant encourage bone healing and bone growth, while stress shielding implants prevent healing, mainly by eliminating the stimuli from the body's osteoblasts.
After a tooth extraction, it is necessary that the site should heal prior to initiating implant procedures. This further extends the time period until the patient is ready to resume normal chewing at the site.
What is needed is an implant system that provides effective attachment to the bone in a shorter period of time than present implants require, and with less inconvenience for the patient during the period when osseointegration takes place.